You don't mention any treatments or medications that have been prescribed to treat your headaches. Have you gotten any meds or treatments?
The reason why they do the CT scan is to rule out any more serious illnesses that you might have, such as multiple sclerosis or a brain aneurysm. Or the blood tests can easily treat other maladies. Many people do not show any clinical reason for their terrible migraines, but they still get treatment. The first most common first step is to give you a daily preventative migraine medication, because taking any pain reliever, even OTC ones, can cause bad rebound headaches.
There are many other medications and other treatments for migraines. So I agree to go to a neurologist or a pain management doctor.
And don't believe that your horrible headaches are from your sinuses. If they are truly horrible, as mine were, two neurologists, a pulmonologist and a second opinion from another ENT doctor, all told me that in no way could my severe migraines be caused by my sinus infection--which I still had.
The first ENT doctor recommended surgery which he said might not help my migraines. He was right, that it would never have helped my migraines.
So get some help treating your migraines.